The Effects of Human Activities on The Ecosystem of Kelp Forests in Norway: A System Dynamics Modelling Approach

Abstract

This thesis aims to contribute to existing knowledge about the ecosystem of kelp forests in Norway. The thesis revolves around the creation of a model that is a simplified conceptual representation of the ecosystem, which I augmented with empirical data and estimates, to make it more realistic and relevant for the Norwegian context. The model values are based on an ecosystem under ideal environmental conditions (from mid-Norway). The model successfully recreates historical trends of the real system, while still maintaining its simplicity. I then identify the main mechanisms that contributes to driving a shift in state from kelp forest to urchin barren. The main mechanism starts with the reliance of gadid fish population on the L.Hyperborea kelp forest to uphold numbers that can counteract an independent population growth of the green sea urchin (S.Droebachiensis). This is because urchins can graze down entire kelp forests within a few years if they are not controlled by predators. This mechanism constitutes a strong reinforcing feedback loop which shifts dominance at thresholds decided by different levels of urchins in the respective states. In Norway, the two leverage points humans have on the ecosystem is kelp trawling and fish harvest, which both can tip the system to change from a kelp forest to an urchin barren. Fish harvest of the coastal gadid fish was found to be the more impactful leverage point of the two. The more pressure humans put on the kelp forest, the more fragile it becomes, proposing that environmental fluctuations that the system otherwise can handle might now push the system beyond its tipping point. I find that with trawl landings of 60% of a local kelp forest, the common 5-year trawling interval could drive the system to a barren state after three trawling periods. With a one-year extension of the interval, to 6 years, the collapse of the kelp forest was avoided. With a predicted increase in kelp trawling, and current trawling landings of up to 75% of local forests, the length of fallow period between each trawling might decide if the forest will collapse or not. The systems knowledge revealed by this thesis and its findings could be used for policy design and to inform decision-making in managing kelp ecosystems.